In order to realize convenient photography operation, various digital cameras adopt optical zoom lens. The optical zoom lens can effectively change the focal length of photography while maintains a good imaging quality thereof. The optical zooming is different from digital zooming whose imaging quality will be adversely affected when the focal length of photography is changed.
U.S. patent application No. US2005/0099700A1 discloses a compact zoom lens comprising four lens groups with positive, negative, positive and positive refraction powers, respectively. When the zoom lens is zoomed from a wide-angle end to a telephoto end, the first and third lens groups remain fixed, while the second lens group moves toward an image side thereof. Although this known zoom lens is relatively compact, it does not provide a high magnification.
A conventional optical zoom lens with a high magnification normally needs a space with a relatively long length for change of focal length. A telescopic lens is such a kind of zoom lens whose lens can be outstretched beyond the body of the camera accommodating it. Most of the digital cameras available on the market use a telescopic zoom lens. The telescopic lens normally adopts one negative lens group, two positive lens groups and three positive lens groups among which a retractable lens group is arranged for zooming operation and this arrangement provides a compact structure. However, the distance required by such a telescopic lens to zoom is inevitably quite long if it aims to acquire a high magnification. Thus, the requirement of the miniaturization cannot be fully met.
A periscope-type zoom lens is another kind of zoom lens having a retractable and extendable lens, which does not need to extend out of the camera accommodating it. The periscope-type zoom lens works in such a way that a light beam entering the lens does not travel along a linear path, and instead, the beam is reflected by a mirror and then refracted into the camera. The lens moves within the camera for zooming or focusing, but does not extend out of the camera. Therefore, the size of a digital camera adopting the periscope zoom lens is much smaller and the camera lens can be effectively protected as there is no need to stretch the lens out of the camera.
Hence, a periscope-type zoom lens is an optimal solution to solve the conflictive and simultaneous requirements of high magnification and miniaturization.
The present invention is thus aimed to provide a novel periscope-type zoom lens.